The present invention relates to an apparatus for interfacing an analog telephone of an integrated services digital network (ISDN) terminal adapter, and particularly to an apparatus for interfacing an analog telephone capable of performing call set-up through an existing analog telephone, independent of the operation of a personal computer.
Generally, an ISDN terminal adapter is installed in expansion slots mounted on a personal computer to use the personal computer as an ISDN terminal, thereby serving as a communication device which intermediates a digital information transfer. The ISDN terminal adapter is connected to network termination equipment via S-interface which has a 2B+D basic access. Here, 2B+D means an ISDN access channel composed of two B-channels and one D-channel. The B-channel is a 64 kbps synchronizing channel for transferring various user information and providing access to the following: a line exchange switching element, a packet exchange switching element for connecting a packet-type terminal, a semipermanent connection-line, and the like. In the ISDN, the D-channel is a 16 kbps channel for transmitting line signal processing information for line exchange switching in an ISDN in accordance with the form of interface, The adapter is operated in a built-in processor by a routine of a protocol processing program, and then performs call set-up and data transmission, etc., which are desirous to ISDN service application programs of a personal computer. Since only a handset, a headset, or a special telephone such as a digital telephone should be utilized to provide audio service besides a digital telephone, existing telephones are not compatible with the ISDN terminal adapters. Because call set-up must be carried out in the personal computer when a handset is the sole provision of the audio service, there is a disadvantage in that operation of the personal computer must be interrupted. Instead of carrying out the call set-up independent of the personal computer when the special telephone is utilized, it is more expensive.